Continuity mistake: There is a scene where Molly Ringwald is confronting her father about lying about seeing a counsellor. His hair is sweaty and messed up a bit and then it changes position to Molly Ringwald and back to her father. Then you will notice that his hair is combed.
Continuity mistake: In outdoor scenes outside of the record shop (mall area), extras are seen on different days in the same outfits.
Continuity mistake: At the end, at the prom, Andrew McCarthy's hair is clearly much shorter (and combed really weird!) than in the rest of the movie. Sure you could argue, "maybe he got a haircut for the prom". But a couple of scenes earlier, it shows everyone getting ready for the prom, including him, and his hair is the same as it is all through the movie, up until the prom scene. [One contributor explains: Andrew McCarthy and Duckie are both wearing wigs. I know this because my father made the wigs. The original ending had Molly Ringwald ending up with Duckie. They wanted to change the ending so that she would end up with McCarthy. In the meantime, he had gotten a crew-cut to appear in a play or movie about soldiers. I don't know what was up w/ Duckie's hair, but the last scene has him in a wig,too].
Deliberate mistake: In the prom scene at the end, there is a shot of a couple dancing with his hand on her rear-end. A counselor comes over and hits the boy's hand to make him move it. He complies, they kiss, and he puts his hand back when the counselor leaves. The camera cuts away to a different shot, and then returns to an over-head wide shot of the crowd. Down in the lower left-hand corner you can see the exact scene with the couple and counselor being filmed.
Continuity mistake: When Andie is yelling at Blaine in the hallway, her purse strap falls off her shoulder at some point. In the next shot, it's back up again and in the next shot it's down, the strap keeps alternating between up and down for the remaining shots.
Continuity mistake: After Blaine is told off by Andi at school, he runs into Steph in the stairwell. Steph is smoking a cigarette, but when he puts it out, it's still almost at full length.
Continuity mistake: When Andie is waiting for Blaine to pick her up from the record store, she's holding a clutch purse. When they are walking to his car, she has a totally different purse on her shoulder.
Continuity mistake: In the scene where Andie and Blaine are talking in their school's courtyard, Andie's shades are in her hand in one shot but automatically appear on her head in the next.
Continuity mistake: During the scene where Andie and Blaine are talking in the "freaks" courtyard, you can see the extra with the black-and-white leggings in the background of each shot. She's behind Blaine, then Andie, then back again instantly throughout the whole conversation.
Continuity mistake: When Blaine goes to the "freak" section of the courtyard, he sits down next to Andie and she takes off her glasses and holds them in her hand. In the very next shot, the glasses are on her head.
Revealing mistake: When Duckie is showing off on his bike, you can see its not Duckie but his stunt double.
